1. Technical Field
The present invention relates to liquid ejecting apparatuses such as an ink jet recording apparatus, and more specifically, liquid ejecting apparatuses having a filter that filters liquid to be supplied to a liquid ejecting head and a filter chamber that houses the filter.
2. Related Art
Typical example of liquid ejecting apparatuses having a liquid ejecting head capable of ejecting a liquid and configured to eject a variety of liquids from the liquid ejecting head include, for example, an image recording apparatus such as an ink jet printer that performs recording by ejecting ink droplets so as to cause the ink droplets to land on a landing target (recording medium) such as a recording sheet. Further, in recent years, such a liquid ejecting apparatus has been applied not only to image recording apparatuses but also to a variety of manufacturing apparatuses. For example, in display manufacturing apparatuses for manufacturing liquid crystal displays, plasma displays, organic EL (electroluminescence) displays, FEDs (field emission displays) or the like, a liquid ejecting apparatus is used to eject a variety of materials in a liquid form such as a coloring material and an electrode material toward a pixel forming region, an electrode forming region or the like.
For example, the above-mentioned ink jet printer is configured to cause ink contained in ink cartridges to be introduced into an ink jet recording head (hereinafter referred to as a recording head), which is a type of liquid ejecting head, and ejected through nozzles of the recording head. It is desirable that ink flow channels (liquid flow channels) extending in the recording head from positions where ink is introduced to the respective nozzles are filled solely with ink. However, air bubbles may be entrained in the ink flow channel during filling (initial filling) of ink into the recording head or exchange of the ink cartridge. Although various measures are taken in this type of printer to prevent the entrainment of air bubbles, it is difficult to completely prevent the entrainment. The air bubbles in the ink flow channel gradually increase in size. When some of the air bubbles which have excessively increased in size move with the ink flow toward a pressure chamber, the air bubbles may clog the ink flow channel or nozzle. This may cause so-called missing dots in which ink is not ejected from the nozzle.
In order to prevent such a problem caused by air bubbles, JP-A-2010-052210 discloses a configuration in which a filter that filters out air bubbles or foreign substances and a filter chamber that houses the filter are provided at a region upstream of the recording head such that the air bubbles are captured by the filter inside the filter chamber.
FIG. 8 schematically shows an ink supply path extending from an ink cartridge 76 to nozzles 73 of a recording head 75 in a printer of the related art. The ink within the ink cartridge 76 is pressurized by an air pump 77 and delivered to a pressure adjustment unit 74 through an ink supply tube 78. The ink which is introduced into the pressure adjustment unit 74 is then directed to pass through a first filter 79 arranged in a first filter chamber 80 and into a pressure adjustment section 84 having a pressure adjustment valve 83 where the ink is depressurized. The ink is further directed to pass through a second filter 81 arranged in a second filter chamber 82 and then supplied to the recording head 75. The pressure adjustment section 84 opens/closes a pressure adjustment valve 83 in accordance with the internal pressure so as to adjust the pressure of ink to be supplied to the recording head 75 at a constant pressure. This can prevent an excessive pressure rise that may cause poor ejection of ink even when the region upstream of the pressure adjustment section 84 is pressurized with a higher pressure than the region downstream of the pressure adjustment section 84.
In the configuration mentioned above, each of the first filter 79 and the second filter 81 are members for filtering ink which flows from the ink cartridge 76 and are formed of, for example, metal wires finely braided into a mesh. Each filter has a number of filter holes. The hole opening size of the second filter 81 which is disposed in the region downstream of the pressure adjustment section 84 is, for example, on the order of 20 μm in diameter so as to prevent air bubbles and foreign matter from being introduced into the recording head 75. The hole opening diameter of the second filter 81 is slightly smaller than the minimum opening diameter of the nozzle 73 (the opening diameter at the ejection surface). Further, the hole opening size of the first filter 79 which is disposed in the region upstream of the pressure adjustment section 84 is, for example, slightly larger than 20 μm in diameter so as to prevent air bubbles and foreign matter from being introduced into the pressure adjustment section 84.
Air bubbles entrained in the ink supplied from the ink cartridge 76 are captured in an upstream side space 85 which is located upstream of the first filter 79 within the first filter chamber 80. Further, air bubbles which have passed through the first filter 79 are captured in an upstream side space 86 within the second filter chamber 82. This enables air bubbles to be prevented from being introduced into the recording head 75 when ink is ejected at the velocity of ejection during a typical recording operation (printing operation) by the recording head 75. Since air bubbles captured in the upstream side space within the filter chamber may increase in size, a cleaning process has been performed to forcibly suction ink or air bubbles from the nozzles 73 by applying a negative pressure to the sealed space by means of a suction pump, which is not shown, with the nozzle surface of the recording head 75 being sealed with the cap member of the capping mechanism 87. This cleaning process enables air bubbles which are captured in the upstream side space within the filter chamber to pass through the filter and to be discharged through the nozzles 73. However, since the hole openings of the conventional filter have a diameter only slightly smaller than the minimum opening diameter of the nozzles 73 (the opening diameter at the ejection surface), air bubbles which have passed through the filter may grow to be larger than the minimum opening diameter of the nozzles 73. This may cause air bubbles to clog a nozzle, resulting in a problem of so-called missing dots in which ink is not properly ejected. In addition, the cleaning process has another problem in that an extra amount of ink is consumed.
The above-mentioned problems exist not only in ink jet recording apparatuses having a recording head that ejects ink, but also in other liquid ejecting apparatuses in which a filter chamber having a filter therein is provided partway along the liquid supply path.